Although there is great concern over emerging viruses and viruses on the NIAID category A-C priority pathogen lists, there are relatively few prophylactics or therapeutics for these viruses, and most which do exist are highly pathogen-specific or have undesirable side effects or other disadvantages. We have developed a radically new and very broad-spectrum antiviral therapeutic/prophylactic that has the potential to revolutionize the treatment of viral infections, including those due to emerging, category A-C, and common clinical pathogens. Our dsRNA (double-stranded RNA) activated caspase (DAC) approach selectively induces apoptosis in cells containing any viral dsRNA, rapidly killing infected cells without harming uninfected cells. We have previously created a DAC and shown that it is nontoxic and effective against 10 different viruses in 10 mammalian cell types. We have also demonstrated that it is nontoxic in mice and rescues mice from a lethal H1N1 influenza challenge. A large number of viruses on the category A-C lists belong to the arenavirus, bunyavirus, and flavivirus families, virus families against which we have not previously tested DAC. Therefore, the experimental focus of this proposal is to test DAC against representative members of these virus families. The specific aims are to: 1. Demonstrate efficacy in multiple mammalian cell types against representative members of the arenavirus, bunyavirus, and flavivirus families. 2. Perform DAC pharmacokinetic analyses and assess DAC immunogenicity in vivo. 3. Demonstrate antiviral efficacy in a lethal mouse model using the best challenge virus from the in vitro trials. Success in these aims should demonstrate the potential of DAC to treat arenaviruses, bunyaviruses, and flaviviruses and pave the way for further trials with additional viruses and animal models. This work should greatly advance DAC toward ultimate utility as a safe, broad-spectrum therapeutic/prophylactic for NIAID priority and emerging viral pathogens, filling a large gap in existing therapeutics and directly supporting NERCE's mission.